1. Field of the Invention
This invention relates, in general, to refrigerating circuit apparatus. In particular, the invention relates to a heat-pump type air conditioning apparatus which carries out a heating or cooling operation by changing the flow direction of refrigerant fed from the compressing device.
2. Description of the Related Art
As is well known, a conventional heat-pump type air conditioning apparatus includes a compressor, a four-way valve, an internal heat-exchanger, an expansion valve and an external heat-exchanger. In such a conventional air conditioning apparatus described above, since refrigerant flowing through the external heat-exchanger absorbs heat from the external air through the external heat-exchanger, frost may adhere to the external heat-exchanger (evaporator) during a heating operation when the external temperature decreases in winter. This is because temperature of the external heat-exchanger decreases, and moisture in the external air condensates and adheres on the external heat-exchanger. The frost accumulated on the external heat-exchanger causes a decrease in the heat-exchange ability of the external heat-exchanger, resulting in the decrease in the heating ability of the air conditioning apparatus. Thus, a defrosting operation should be carried out regularly. In the conventional heat-pump type air conditioning apparatus, the defrosting operation is carried out by changing the direction of the refrigerant fed from the compressor to remove frost built up on the external heat-exchanger. Such defrosting operation is called a reverse cycle defrosting operation. However, in the reverse cycle defrosting operation, since heat in an internal space to be air conditioned is absorbed by refrigerant flowing through the internal heat-exchanger, the heat absorption efficiency of the apparatus is relatively low, and therefore, the defrosting time may be long. This is because the internal temperature may be reduced because of interruption of the heating operation if the reverse cycle defrosting operation is carried out during the heating operation. Furthermore, the internal fan device which supplies air to the internal heat-exchanger is stopped during the reverse cycle defrosting operation to avoid a rapid temperature decrease in the internal space.
In the above-described heat-pump type air conditioning apparatus, a two stage compressor may be used to vary the compressing capacity. The two stage compressor includes a lower stage compressing device and an upper stage compressing device serially connected with one another to easily change the compressing capacity at multiple steps. The two stage compressor operates at a high efficient rate. However, in such air conditioning apparatus using the above-described two stage compressor, the heating operation also is interrupted during the execution of the defrosting operation if the above-described reverse cycle defrosting operation is adapted to the air conditioning apparatus. It is desirable to perform the defrosting operation in parallel with the heating operation. However, in the type of air conditioning apparatus described above, many components and a complicated control system are required to assure that the heating operation is continued even if the defrosting operation begins.